November 11, 2005

mtDNA of early central European farmers

A new study in Science examines ancient mtDNA from Central Europe and more precisely from the Linearbandkeramik (LBK) and the related Alföldi Vonaldiszes Kerámia (AVK) cultures. The farmers of the LBK are responsible for the spread of agriculture in Central and Northern Europe, and hence their genetic composition is of particular interest:

From a total of 57 LBK/AVK individuals analyzed, 24 individuals (42%) revealed reproducibly successful amplifications of all four primer pairs from at least two independent extractions usually sampled from different parts of the skeleton. Eighteen of the sequences belonged to typical western Eurasian mtDNA branches; there were seven H or V sequences, five T sequences, four K sequences, one J sequence, and one U3 sequence (table S1). These 18 sequences are common and widespread in modern Europeans, Near Easterners, and Central Asians, and thus these 18 lineages lack the detailed temporal or geographic discrimination required to test the hypotheses we are examining, even though some of them have previously been suggested to be of Neolithic origin on the basis of modern DNA studies (15). We therefore concentrated on the mtDNA types identified in the other six individuals.

The most striking result is that 6 of the 24 Neolithic skeletons are of the distinctive and rare N1a branch. For verification, we sequenced 517 clones derived from independent extractions from different parts of the six individuals. All six showed the suite of mutations characteristic of the N1a lineage. Five of these six individuals display different N1a types, whereas Flomborn 1 and Derenburg 3 show identical N1a types (Table 1).

It is not surprising that the early Neolithic farmers belonged mainly to several well-known Caucasoid haplogroups. What is surprising is that a particular lineage, N1a which occurs at a low frequency in modern Europeans was found at a very high frequency in the ancient farmers. Moreover, it occurred in different sites, hence it appears to be a genuine distinguishing feature of the LBK, and not simply a peculiarity of some local population.

The reduction of frequency of N1a in the modern sample is 150-fold. As the authors suggest, genetic drift alone cannot account for this enormous reduction, and the reduction can be explained either because (a) modern central Europeans are primarily descended from Paleolithic ones and not from the Neolithic culture bearers, or (b) the genetic legacy of the early farmers has been wiped out by subsequent population movements into Central Europe:

These simulations reject the simple hypothesis in which modern Europeans are direct descendants of these first farmers and have lost N1a mainly by genetic drift. Hence the simulations confirm that the first farmers in Central Europe had limited success in leaving a genetic mark on the female lineages of modern Europeans. This is in contrast to the success of the Neolithic farming culture itself, which subsequently spread all over Europe, as the archaeological record demonstrates. One possible explanation is that the farming culture itself spread without the people originally carrying these ideas. This includes the possibility that small pioneer groups carried farming into new areas of Europe, and that once the technique had taken root, the surrounding hunter-gatherers adopted the new culture and then outnumbered the original farmers, diluting their N1a frequency to the low modern value. Archaeological research along the Western periphery of LBK and isotope studies of some of our sampled individuals seem to support the idea that male and female hunter-gatherers were integrated into the Neolithic communities (3, 10, 29). This hypothesis implies that N1a was rare or absent in Mesolithic Europeans, which may be a reasonable assumption given the rarity of the N1a type anywhere in the world (Fig. 3). An alternative hypothesis is a subsequent post–early-Neolithic population replacement in Europe, eliminating most of the N1a types. Archaeological evidence for such an event is as yet scant.

In the supplemental data we can see that there are some modern matches to the 6 ancient mtDNA sequences belonging to haplogroup N1a.

The sequence of Derenburg 3/Flomborn 1 occurs in the Chuvashi, in Slovakia, in Yemen, in Mashhad \Ostan-e-Khorasan, in Turkmen from Turkmenistan, in Iran, in Estonia, and in Sweden

The sequence of Derenburg 1 occurs in Cairo Egypt, and Armenia.

The sequence of Halberstadt 2 is not found elsewhere.

The sequence of Unterwiederstedt 5 is not found elsewhere.

The sequence of Ecsegfalva 1 is not found elsewhere

In conclusion, it appears that modern central Europeans are very little physically descended from the early Neolithic culture bearers of the same region. What we really need now is for other early Neolithic samples from other parts of Europe, Western Eurasia, and Northern Africa to be studied, to see whether N1a was a peculiarity of the LBK, or it was a genuine feature of the first farmers.

PS: It should be noted that an alternative explanation for the great reduction in the frequency of N1a would be some form of negative selection. This suggestion is entirely speculative, but it should be kept in mind.

Update 2: The major weakness of the study -apart from not having anything to say about selection- is that it assumes that haplogroup N1a was brought into Central Europe by the Neolithic farmers. However, there is no reason to suppose that this is the case. The authors arbitrarily label N1a as Neolithic, but they have no evidence that N1a was brought by the immigrant farmers and does not represent an indigenous component. Indeed, their own map shows that the particular cluster of N1a found in modern Europeans is not found in Greece or Turkey where the Neolithic of Europe originated. So, it is just as likely that N1a may be indigenous to central Europe and the Neolithic was associated with some of the other 18 sequences that were found in the Linear Pottery sample. Indeed, if N1a turns out to be Paleolithic, then the conclusions of their study will be completely reversed, and the great decrease in frequency of N1a would indicate an almost complete replacement of Paleolithic people by Neolithic farmers.

In conclusion: the authors don't present any evidence for N1a being Neolithic by either measuring a high frequency in originary areas of the Neolithic (Anatolia and Greece), or by sampling ancient populations from the originary areas. Hence, their conclusions are entirely arbitrary.

Science, Vol 310, Issue 5750, 1016-1018 , 11 November 2005

Ancient DNA from the First European Farmers in 7500-Year-Old Neolithic Sites

Wolfgang Haak et al.

The ancestry of modern Europeans is a subject of debate among geneticists, archaeologists, and anthropologists. A crucial question is the extent to which Europeans are descended from the first European farmers in the Neolithic Age 7500 years ago or from Paleolithic hunter-gatherers who were present in Europe since 40,000 years ago. Here we present an analysis of ancient DNA from early European farmers. We successfully extracted and sequenced intact stretches of maternally inherited mitochondrial DNA (mtDNA) from 24 out of 57 Neolithic skeletons from various locations in Germany, Austria, and Hungary. We found that 25% of the Neolithic farmers had one characteristic mtDNA type and that this type formerly was widespread among Neolithic farmers in Central Europe. Europeans today have a 150-times lower frequency (0.2%) of this mtDNA type, revealing that these first Neolithic farmers did not have a strong genetic influence on modern European female lineages. Our finding lends weight to a proposed Paleolithic ancestry for modern Europeans.

1 comment:

As I have stated numerous times, one has to be very careful when trying to interpret ancient European neolithic mtDNA in a framework of migrations - especially if based on extant distributions.

I have voiced my criticism of Haak many times before.

There are several forces at play why today mtDNA is so different from ancient LBK:

- the HG revenge (when neolithic farmers faced climatic and disease problems due to severe crop and livestock inbreeding, outside HGs were ready to take their place)

- LBK mtDNA really is predominantly Balkan - not near-Eastern, and picked up additional lineages along their way (e.g., from the Danube and Black Sea, some of them Central or eastern Asian)

- some lineages are just happenstance in a rapidly exploding population (N1a)

It's not black or white in terms of HGs and Neolithic folks, but one also has to keep in mind that during the Mesolithic, there were local pockets from quite different refugium origin, and Northern/Central Europe surely was different from SE Europe, and the Mediterranean from the North, and Iberia from Italy or the Balkans.

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